This application claims the priority of 01006427.6, filed in Europe on Mar. 22, 2002, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a two-medium spraying nozzle, particularly for atomizing low-viscosity fluids for the cooling of continuous-casting systems, having a housing with a mixing chamber and having one connection duct respectively leading into this mixing chamber, for the feeding of a gaseous and a liquid medium, as well as having a mouthpiece connected downstream of the mixing chamber in the flow direction, the mouthpiece having an axial cylindrical bore and a rotationally symmetrical outlet opening.
In continuous-casting systems, a two-medium secondary cooling is provided for the production of steel billets or blooms. This two-medium secondary cooling is achieved predominantly by means of two-medium full-cone nozzles with an internal mixing of the media. Thus, for example, pneumatic atomizer nozzles of the 138.XXX series are known for this purpose, which are sold by the applicant (Lechler Katalog, xe2x80x9cDie ganze Welt der Dxc3xcsen technikxe2x80x9d (xe2x80x9cComplete World of Nozzle Technologyxe2x80x9d, Edition 921, Print Note xe2x80x9cKat./10.92/D, E, F, GB/5000xe2x80x9d, Page 1.28). These full-cone pneumatic atomizer nozzles, which operate according to the hydrostatic pressure principlexe2x80x94the air pressure is kept constantxe2x80x94, are provided with a cylindrical mixing chamber. The air current leads axially into this cylindrical mixing chamber and tears apart into fine droplets a liquid (water) jet guided transversely to the air current into the mixing chamber. From the mixing chamber, the two-medium mixture is then guided through a ring duct to an also ring-shaped outlet opening which is formed by an opening of a larger diameter than a ring space and arranged at the lower end of the ring space coming out of the mixing chamber and by a rebounding plate centrally held in this opening. In this case, the rebounding plate is held by way of a central shaft in a mouthpiece provided with the outlet opening, and the ring-shaped outlet duct is formed on the inside by the shaft of the rebounding plate and on the outside by the wall of the mouthpiece. The two-medium mixture, which is formed largely homogeneously already in front of the outlet duct in the mixing chamber, when axially flowing through the mouthpiece, will then impact on the rebounding plate and will be conically delivered to the outside in the shape of a full-cone spraying jet.
In the case of such pneumatic atomizer nozzles, the actual ring-shaped outlet opening between the outer edge of the rebounding plate and the outlet opening of the mouthpiece is constructed only as a very narrow ring of a width of in the order of 0.7 mm. Nozzles of this type therefore tend to clog at the outlet when the operating media, that is, the air and the water can no longer be kept clean, which naturally takes place in the production of steel. Nozzles of this construction also demand very low manufacturing tolerances and exhibit, also along the entire pressure range, that is, when the hydrostatic pressure is changed, a considerable change of the spraying angle, in which case also the full-cone character cannot be maintained over the entire control range.
It is therefore an object of the present invention to develop a two-medium spraying nozzle of the initially mentioned type such that the nozzles become unsusceptible to clogging and can be used in the entire control range while the air consumption is low and the spraying angle is stable. This has the purpose of covering the product spectrum for the manufacturing of high-quality steel types which is wider in the case of modern continuous-casting systems. The two-medium spraying nozzles should in each case be adaptable to the width of the products to be manufactured without causing an overcooling.
For achieving this object, the invention comprises arranging a swirl insert in the bore of the mouthpiece and providing the outlet opening centrally on the bottom of the mouthpiece with a diameter which corresponds to no more than half the diameter of the bore of the mouthpiece.
This further development permits the arrangement of a relatively large outlet opening which is unsusceptible to clogging. Astonishingly, it was found in this case that the swirl insert arranged in the mouthpiece, does not, as was to be feared, act in the manner of a drop collector and cancel out again the desired intimate and homogeneous mixing of liquid and air. However, the swirl insert provides that the gas-liquid mixture is caused to rotate before reaching the outlet opening so that it can then under pressure exit conically from the mouthpiece. It was found that, by means of this construction, the spraying angle becomes significantly less dependent on the variable hydrostatic pressure. The nozzle is also unsusceptible to dirtying.
In a further development of the invention, the outlet opening may expand to an outlet cone whose outlet angle is adapted to the desired spraying angle. The portion of the bottom of the mouthpiece surrounding the outlet opening may in this case be aligned in a flat and rectangular manner to the axis of the bore. However, it is also contemplated that the portion of the bottom surrounding the outlet opening is rounded.
As a further development of the invention, the swirl insert may be drilled or milled and may be provided with several bores or with several milled slots arranged at the circumference which are uniformly distributed along the circumference. It was found that very good results can be achieved by means of such a swirl insert and that, as mentioned above, the feared separation of the two-medium mixture has not occurred. As a further development of the invention, the swirl insert was also provided with an axially extending center bore which has an inlet and outlet chamfer. This center passage opening, which is mounted in a centric manner, has a positive influence on the symmetry of distribution.
As a further development of preferred embodiments of the invention, it is expediently taken into account that the sum of the free cross-sections of all bores provided in the swirl insert or the sum of the free passage cross-sections of the center bore and of the passage slots milled in on the outside are larger than the passage cross-section of the outlet opening of the mouthpiece. This further development leads to the rotation of the two-medium mixture upstream the outlet opening and ensures the formation of the desired full-cone jet.
As a further development of preferred embodiments of the invention, the distance between the bottom of the mouthpiece and the swirl insert is in each case selected such that a homogeneous flow is achieved upstream of the outlet opening which no longer has the influences of the individual jets passing through the bores.
As a further development of preferred embodiments of the invention, the mixing chamber may have a cylindrical construction with connection ducts situated perpendicular with respect to one another, the mouthpiece being constructed as a screwed sleeve which is connected directly downstream of the mixing chamber. However, it is also contemplated to construct the mixing chamber such that the connection duct for the liquid leads into the mixing chamber by way of a nozzle, which mixing chamber is provided on the wall opposite this nozzle with an indentation as a rebound surface for the liquid jet coming from the nozzle, the air connection extending in the axial direction of the mixing chamber and perpendicular to the axis of the liquid jet. In this embodiment, an extension pipe can be provided between the mouthpiece and the mixing chamber, as in the case of other constructions (German Patent Document DE 195 05 647). In this case, the mouthpiece can be fastened by way of a union nut on the extension pipe.
The invention will be illustrated by means of two embodiments in the drawing and will be explained in the following.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.